By Ellen Nakashima

11 March 2014 — 11:22am

Washington: America's spy agencies are so focused on "mass surveillance" that they have missed clues about terrorist incidents, such as last year's Boston Marathon bombing and an attempted attack on an aircraft at Christmas in 2009, former intelligence contractor Edward Snowden says.

In an hour-long video discussion on Monday hosted by the South by Southwest music, film and technology conference in Austin, Texas, Mr Snowden, who is living in asylum at an undisclosed location in Russia, asserted that the US National Security Agency's efforts to collect information in bulk have backfired.

"We've actually had a tremendous intelligence failure because ... we're monitoring everybody's communications instead of suspects' communications" - a situation, he asserts, that has "caused us to miss" intelligence.

Mr Snowden, who faces criminal espionage charges for disclosing top-secret documents to journalists, has prompted a global debate about surveillance and forced the US government to be more transparent about once-classified programs.

His actions have drawn harsh criticism from senior US officials, who contend that the leaks have put national security at risk, but approval from technologists and privacy advocates, who say the leaks have forced technology companies to make their systems more secure.

"Let me be clear about one thing," said American Civil Liberties Union principal technologist Christopher Soghoian, one of two ACLU representatives who took part in the discussion with Mr Snowden: "His disclosures have improved internet security."

Mr Snowden, who was using a Google videoconferencing program that ran through seven proxy servers to mask his location, used much of his talk to urge companies and technologists to develop and adopt easier-to-use encryption. "It has to happen seamlessly," he said.

If "you encrypt your hardware and your network", Mr Snowden said, "it becomes very difficult for any mass surveillance ... You'll still be vulnerable to targeted surveillance. If there's a warrant for you, the NSA will still get you."

Edward Snowden on screen at the South by Southwest festival in Austin, Texas.Credit:Bloomberg

Encryption, he said, enabled him to protect the information he took from the NSA, where he worked until last year. US officials "still have no idea of what documents were provided to journalists, what they have and don't have", he said, "because encryption works".

He also said that neither the Chinese nor the Russian governments possess any of the information he took.

The intelligence failures Mr Snowden alleged are not clear-cut. The Christmas 2009 bomb attempt involved a failure to connect and understand the information agencies possessed. In the Boston case, the FBI followed up on a tip from Russian authorities about a suspect but found insufficient grounds to open a criminal investigation.

General Keith Alexander, the outgoing director of the NSA, has vigorously defended the agency's activities. "The press has articulated them as the villains, when what they're doing is protecting this country and doing what we have asked them to do," he told US Congress last month. "And if they've made a mistake, we find out.''

During the videoconference, an image of the US constitution provided a background for Mr Snowden. The session was conducted by ACLU lawyer Ben Wizner, Mr Snowden's legal adviser.

Asked by Mr Wizner whether the price he has paid for his disclosures has been worth it, Mr Snowden said: "Regardless of what's happening to me, this is something we have a right to know. I took an oath to support the constitution, and I felt the constitution was violated on a massive scale. The interpretation of the constitution has been changed in secret from 'no unreasonable search and seizure' to: 'Hey, any seizure is fine. Just don't search it.' That's something the public ought to know about."